The present invention relates to printing plate clamping apparatus, and, more particularly, to apparatus for clamping flexible thin printing plates in position on a press cylinder. The present invention is primarily directed to an improved arrangement for clamping such thin flexible printing plates into position directly on the press cylinder, as well as on shim members, which shim members are detachably or non-detachably attached to a press cylinder for radially positioning the printing plate with respect to the surface of the press cylinder. Such shim members are utilized in conjunction with existing presses made for earlier used very thick lead stereotype plates. In other words, the shim members serve to account for the difference in thickness between the thin flexible printing plate now generally used and the earlier lead stereotype plates.
U.S. Pat. No. 3,791,295 to Albright discloses a known apparatus for clamping thin flexible printing plates on a press cylinder. In Albright, one extreme circumferential edge portion of the thin printing plate is clamped by a spring loaded clamping bar. In order to attach a printing plate to the saddle member of Albright, one must force the clamping bar against the springs to a non-clamping position, while one simultaneously places the thin printing plate in position to be clamped, at which time the clamping bar is released to resiliently clamp the printing plate. This Albright arrangement is disadvantageous in that it is very difficult, especially with thin flexible printing plates, to simultaneously hold the clamping bar in the non-clamping position and place the printing plate in a position to be clamped in a reliable manner.
The present invention overcomes the above-noted disadvantage, by providing a retaining system for retaining the clamp bar in a non-clamping position, which retaining system does not require continuous manual holding of the clamping bar in this non-clamping position. One can then have both hands free to place the printing plate in position to be clamped, after which a simple releasing operation accommodates the automatic resilient biasing of the clamping bar into the clamping position.
In preferred embodiments of the present invention, it is contemplated to provide retaining straps attached to the clamping bar, which retaining straps are engageable with a spring loaded release bar for locking said straps and clamping bar in the non-clamping position. The release bar is continuously spring biased in a locking direction such that, upon movement of the clamping bar to the non-clamping position, the release bar automatically locks the same in said non-clamping position. To accommodate release of the retaining mechanism, the release bar extends outwardly at one end of the press cylinder so as to be manually engageable at a push-button end thereof, whereby one merely needs to push against the release bar against the force of the spring and the retainer straps are released with the automatic movement of the clamp bar into engagement with the printing plate.
In a preferred embodiment of the present invention, the retainer straps are attached by screws to the clamp bar and extend away from the clamp bar in the circumferential direction of the saddle or press cylinder. At a position spaced from the clamp bar, the straps are provided with cutout detent grooves engageable by detent pin members carried by a release bar which extends transverse to the direction of movement of said straps and clamp bar. The release bar is spring loaded to force the detent pins thereof into the detent grooves in the retainer straps whenever the retainer straps are circumferentially aligned therewith. Also in preferred embodiments, the retainer straps are guided for movement by retainer screws extending through guide slots in the retainer straps.
Preferred embodiments of the invention are particularly adapted for use with saddle members that are detachably connected to the press cylinder. However, other preferred embodiments are contemplated where the clamping assembly and the retaining assembly are provided at the press cylinder itself, in instances where the press cylinder is of a construction so that the saddle members are not needed to radially space the thin flexible printing plates.
These and further objects, features and advantages of the present invention will become more apparent from the following description, when taken in conjuction with the accompanying drawings and claims.